ERCOT Dynamic Model Improvements Under PGRR 085:

Raising the Standard for Model Accuracy, Validation, and Hardware Benchmarking in ERCOT

Executive Overview

Accurate dynamic models are the foundation of reliable grid planning and operations. With increasing penetration of inverter-based resources (IBRs), energy storage resources (ESRs), and advanced transmission equipment, modeling errors no longer result in minor study discrepancies — they can create real operational risks.

PGRR 085 – Dynamic Model Improvements strengthens ERCOT Planning Guide Sections 5.7.1 and 6.2 by introducing:

• Mandatory model quality testing
• PSCAD hardware benchmarking
• Parameter verification reports
• Defined submission timelines
• Cross-platform consistency requirements (PSS®E and PSCAD)



This revision directly supports Reliability and Operations Subcommittee (ROS) goals to improve dynamic modeling processes 

Why PGRR 085 Was Necessary

Historically, planning models often differed from:

• Actual field-implemented settings
• Hardware performance
• Behavior across simulation platforms



ERCOT uses:

• PSS®E for general planning stability studies
• PSCAD for weak grid and subsynchronous resonance (SSR) analysis
• 
  

PGRR 085 formally establishes the expectation that model response shall be consistent across platforms to the extent of platform capability 

The business case identifies three major goals 

1. Ensure consistency between model software platforms
2. Ensure accuracy between models and actual hardware
3. Ensure ERCOT uses high-quality, accurate system models

Major Requirements Introduced by PGRR 085

1. Dynamic Model Submittals During FIS

Under Section 5.7.1, Interconnecting Entities (IEs) must provide:

• Appropriate dynamic models
• Results of model quality tests
• Associated simulation files
• Compatibility with ERCOT standard tools (PSS®E, TSAT, VSAT, SSAT) 

If no compatible model exists:

• The IE must work with vendors or consultants
• The model must be incorporated into standard libraries 

This eliminates proprietary black-box barriers to system-wide modeling.

2. Model Quality Testing (Section 6.2)

Whenever a new or updated dynamic model is submitted, model quality testing is required.

Required Tests

A. Flat Start Test

Validates:

• Proper initialization
• No oscillations under no-disturbance conditions

B. Small Voltage Disturbance Test

Applies:

• Step increase and decrease at POI
  Demonstrates voltage control and reactive response.

C. Large Voltage Disturbance Test

• For IBRs/ESRs → Apply VRT profile
• For synchronous machines → Apply fault at POI 

D. Small Frequency Disturbance Test

Step change in frequency to test governor/active power response.

E. System Strength Test

IBRs must be tested under varying short circuit ratios .

This ensures:

• Stability under weak grid conditions
• Robust inverter controls
  

3. PSCAD Hardware Benchmarking for IBRs

IBRs must provide unit model validation results demonstrating that the PSCAD model accurately represents inverter hardware behavior through structured PSCAD model validation for inverter-based resources.

Required PSCAD validation tests include:

• Voltage step response
• VRT testing
• System strength testing
• Phase angle jump test
• Subsynchronous test 

These tests are hardware-type based and may be reused across projects using the same inverter model.

This is a major reliability enhancement.

4. Parameter Verification Reports

Facility owners must provide verification reports confirming:

• Model parameters match field-implemented settings
• Site-specific tuning values are documented 

Required Timeline



For Generation Resources and ESRs 

• At commissioning
• 12–24 months after commissioning
• Every 10 years minimum
• After settings changes

For Transmission Elements:

• Within 2 years of energization
• Every 10 years thereafter
  

5. Ongoing Obligations

Resource Entities must provide updated dynamics data when:

• Equipment is replaced
• Settings are changed
• Field tests indicate model inaccuracies 
  

Implications for Inverter-Based Resources (IBRs)

IBRs face the most rigorous requirements:

• PSCAD hardware validation
• System strength testing
• Aggregated modeling requirements
• VRT performance validation
• Cross-platform consistency



Given the grid’s shift toward inverter dominance, this is both necessary and overdue

Implications for Transmission Service Providers (TSPs)

TSPs must provide dynamic models for:

• Load shedding relays
• FACTS devices (SVC, STATCOM)
• DC ties
• VFTs
• Tap-changing transformers 



This creates modeling parity between generation and transmission.

Why This Matters for Reliability

Poor dynamic modeling can result in:

• Undetected instability
• Overestimated short circuit strength
• Inaccurate SSR analysis
• Improper reactive planning
• Misleading stability margins

PGRR 085 directly addresses these risks.

Engineering Best Practices for Compliance

To align with PGRR 085:

1. Maintain a model governance program
2. Track site-specific tuning parameters
3. Align commissioning reports with model parameters
4. Maintain PSCAD and PSS®E version control
5. Develop repeatable model test scripts
6. Schedule periodic model audits
   

The Long-Term Impact

PGRR 085 moves ERCOT toward:

• Hardware-aligned modeling
• Cross-platform validation
• Lifecycle compliance
• Stronger weak-grid analysis
• Higher confidence in interconnection studies



As IBR penetration increases, these requirements will become industry standard.

25 Technical FAQs on PGRR 085 Dynamic Model Improvements